Wavelength tunable MEMS-Fabry Perot filter

Abstract

A wavelength tunable gain medium with the use of micro-electromechanical system (MEMS) based Fabry-Perot (FP) filter cavity tuning is provided as a tunable laser. The system comprises a laser cavity and a filter cavity for wavelength selection. The laser cavity consists of a gain medium such as a Semiconductor Optical Amplifier (SOA), two collimating lenses and an end reflector. The MEMS-FP filter cavity comprises a fixed reflector and a moveable reflector, controllable by electrostatic force. By moving the MEMS reflector, the wavelength can be tuned by changing the FP filter cavity length. The MEMS FP filter cavity displacement can be tuned discretely with a step voltage, or continuously by using a continuous driving voltage. The driving frequency for continuous tuning can be a resonance frequency or any other frequency of the MEMS structure, and the tuning range can cover different tuning ranges such as 30 nm, 40 nm, and more than 100 nm.

What is claimed is: 
     
       1. A tunable MEMS-FP filter comprising:
 a semiconductor or dielectric substrate, transparent to light in the wavelength range 100-3000 nm, having an upper and a lower face; 
 a fixed reflector configured to accept input light, and attached to the lower face of the substrate; 
 a bottom electrode disposed on the upper face of the substrate; 
 an AR layer disposed on the upper face of the substrate; 
 a moveable reflector having an upper and a lower face, supported by one or more suspension beams, and comprising a MEMS and multilayer dielectric DBR mirrors and a top electrode disposed on the upper face of the moveable reflector, wherein an air gap is formed between the lower face of the moveable reflector and the upper face of the substrate; 
 wherein an optical cavity is formed between the fixed reflector and the moveable reflector, and the optical cavity includes a portion of the substrate between the fixed reflector and the bottom electrode; and 
 a voltage source to supply voltage between the top electrode and the bottom electrode to change the cavity length of the optical cavity. 
 
     
     
       2. The tunable MEMS-FP filter of  claim 1 , wherein the multilayer DBR mirrors are comprised of: Si/SiO 2 , Si/Al 2 O 3 , SiO 2 /TiO 2  or Ta 2 O 3 /SiO 2 . 
     
     
       3. The tunable MEMS-FP filter of  claim 1 , wherein the substrate is comprised of a semiconductor or dielectric material selected from: Si, InP, GaAs, or GaP. 
     
     
       4. The tunable MEMS-FP filter of  claim 1 , wherein the fixed reflector comprises a high reflective (HR) coating layer. 
     
     
       5. The tunable MEMS-FP filter of  claim 1 , wherein the fixed reflector comprises multilayer dielectric DBR mirrors. 
     
     
       6. A free space linear cavity tunable laser source comprising the tunable MEMS-FP filter of  claim 1 . 
     
     
       7. The tunable laser source of  claim 6 , further comprising a gain medium, two lenses, and an end reflector. 
     
     
       8. The tunable laser source of  claim 7 , wherein the gain medium is a SOA. 
     
     
       9. A fiber coupled ring cavity tunable laser source comprising the MEMS-FP filter of  claim 1 , a fiber coupled gain medium, and a fiber optics coupler. 
     
     
       10. The fiber coupled ring cavity tunable laser source of  claim 9  wherein the gain medium is a SOA. 
     
     
       11. The tunable MEMS-FP filter of  claim 1 , wherein the semiconductor or dielectric substrate is transparent to light in the wavelength range 600-1800 nm. 
     
     
       12. The tunable MEMS-FP filter of  claim 1 , wherein the MEMS comprises multilayer dielectric DBR mirrors. 
     
     
       13. The tunable MEMS-FP filter of  claim 1 , wherein the moveable reflector comprises a MEMS structure and a high reflective (HR) coating layer. 
     
     
       14. The tunable MEMS-FP filter of  claim 1 , wherein the thickness of the portion of the substrate is variable. 
     
     
       15. The tunable MEMS-FP filter of  claim 14 , wherein the free spectral range (FSR) can be varied by varying the thickness of the portion of the substrate independently from variations in the length of the air gap. 
     
     
       16. A tunable MEMS-FP filter, comprising:
 a semiconductor or dielectric substrate, transparent to light in the wavelength range 100-3000 nm, having an upper and a lower face; 
 a fixed reflector configured to accept input light, and attached to the lower face of the substrate, 
 a bottom electrode disposed on the upper face of the substrate; 
 an AR layer disposed on the upper face of the substrate; 
 a moveable reflector having an upper and a lower face, supported by one or more suspension beams, and comprising multilayer dielectric DBR mirrors and a top electrode disposed on the upper face, wherein an air gap is formed between the lower face of the moveable reflector and the upper face of the substrate; 
 wherein an optical cavity is formed between the fixed reflector and the moveable reflector, and the optical cavity includes a portion of the substrate between the fixed reflector and the bottom electrode; and 
 a voltage source to supply voltage between the top electrode and the bottom electrode to change the cavity length of the optical cavity. 
 
     
     
       17. The tunable MEMS-FP filter of  claim 16 , wherein the fixed reflector comprises a high reflective (HR) coating layer. 
     
     
       18. The tunable MEMS-FP filter of  claim 16 , wherein the semiconductor or dielectric substrate is transparent to light in the wavelength range 600-1800 nm.